Just found out my boyfriend is still smoking even though he said he quit.

So my bf had to move back in with his dad to help him out for a little bit and his dad smokes so I didn't think much of find packa there at first. Until I started to notice them more around where my boyfriend would spend his time. I asked him about it and he said his friend would come over and smoke while they hung out. Then today I found out from his brother that he's been smoking again and I just don't know what to do. He had quit before we started dating and I'd told him beforehand that I'd never date a smoker.... :/